1. Field of the Invention
The present invention relates to a pen, for example, a ballpoint pen, a correction pen, a sizing pen, and particularly to a pen adapted to be pressurized (hereinafter pressurization pen), which is capable of smoothly supplying a medium such as ink, correction fluid, paste, etc., when using the pen.
2. Description of the Related Art
The known pen, for example, a ballpoint pen has been experienced a disadvantage that ink does not smoothly outflow from a pen tip of a pen refill unit in use or ink is interrupted during writing, so that when such problem is occurred, it is necessary to scrub the pen tip on a paper to outflow the ink.
To overcome such disadvantage, as disclosed in Japanese Patent Publication JP-A-2004-268567 (FIGS. 3 and 4) and Japanese Patent Publication JP-A-2005-178304 (FIGS. 3 and 4), it has been suggested that a pen refill unit of a ballpoint pen is provided with a pressurizing pump mechanism and an inside of ink accommodating tube filled with ink is pressurized through the operation of the pressurizing pump mechanism in the related art.
However, in the known ballpoint pen of any of above described patent documents, the inside of the ink accommodating tube is sealed to maintain always the pressurized state after the inside of the ink accommodating tube of a pen refill unit is pressurized by the pressurizing pump mechanism. In this state, when the pressurizing pump mechanism is repeatedly operated, the inside of the ink accommodating tube becomes an excessive pressurized state so that the ink leakage may easily occur to contaminate a pen holder, and hence hands or clothes. In addition, there is further disadvantage that in order to maintain the inside of the ink accommodating tube in a high airtight state, materials of seal parts and the processing precision are required, thereby increasing a cost.